1. Field of the Invention
The present invention relates to an external-force detecting apparatus used to detect, for example, an angular velocity and a method of detecting line break for the external-force detecting apparatus.
2. Description of the Related Art
Recently, vibrating gyroscopes have been used to detect the orientation of a vehicle, to detect the traveling direction of a navigation apparatus, to correct motion blur of a camera caused by hand shake, to operate the virtual reality, and to perform other suitable functions. As an example of such a vibrating gyroscope, for example, Japanese Unexamined Patent Application Publication No. 2006-170620 (Japanese Unexamined Patent Application Publication No. 2006-170620) discloses the following gyro sensor. Two drive signals defined by sine waves having opposite phases are applied to two respective drive electrodes in a sensing element in order to drive a movable electrode. The variation in capacitance of two monitor electrodes arranged to monitor the vibrating state of the sensing element is converted into two respective monitor signals by a capacitance voltage (CV) converter and the two monitor signals are supplied to a variable gain amplifier. The variable gain amplifier controls the conversion factor in voltage-current conversion so that the two monitor signals have a certain amplitude.
With the gyro sensor described in Japanese Unexamined Patent Application Publication No. 2006-170620, for example, if either of the two lines connecting a drive buffer and the drive electrodes is broken, the sensing element can be normally driven. Specifically, for example, if either of the two lines connecting the drive buffer and the drive electrodes is broken, the amplitude of the drive signals is reduced by half and the drive level of the sensing element is also reduced by half. In addition, the amplitude of the two monitor signals supplied to the variable gain amplifier is reduced by half. Since the variable gain amplifier doubles the conversion factor in the voltage-current conversion, that is, doubles the amplitude of the drive signals applied to the drive electrodes so that the monitor signals have a certain value, the sensing element is normally driven. Accordingly, the gyro sensor described in Japanese Unexamined Patent Application Publication No. 2006-170620 has a problem in that it is not possible to detect when a line connecting the drive buffer to the drive electrodes is breaks.